This invention relates to electron multipliers, and particularly to a multiplier structure having channels for confining the flow of electrons therethrough in which additional means are provided for establishing a high multiplier gain condition in an "on" channel while simultaneously establishing a low gain condition in channels adjacent thereto.
Display devices have been proposed in which electron multipliers operated in a feedback mode are used to provide current to light up a cathodoluminescent screen. For example, see U.S. Pat. No. 3,904,923 entitled, "Cathodoluminescent Display Panel", issued Sept. 9, 1975 to J. Schwartz. In one such structure, the electron multiplier includes at least two vanes having a plurality of parallel dynodes in staggered relation thereon with a cathode at one end. This structure is further described in copending application of Endriz et al, Ser. No. 672,122, filed Mar. 21, 1976 entitled, "Parallel Vane Structure for a Flat Display Device." In this structure, electrical potentials of increasing magnitude are provided to the successive multiplying dynodes so as to produce an electron beam at the multiplier output. Generally, the electron multiplier has an open structure to allow feedback of ions which results in sufficiently high loop gain to produce sustained electron emission.
A requirement of such a display is that the electron beam be confined to an area of the screen which is no larger than one picture element. However, in the previously described electron multipliers, spreading of the electron beam occurs in a direction along the length of the dynodes. This spreading problem is substantially attenuated by the use of a nonplanar dynode structure wherein confinement bumps help to confine the flow of electrons through predetermined channels. Further information on the confinement bump structure and operation are found in copending application, Ser. No. 714,358, entitled "Electron Multiplier with Beam Confinement Structure," by Catanese and Keneman, filed Aug. 16, 1976, now U.S. Pat. No. 4,041,342 which is hereby incorporated by reference.
Although the confinement structure shown in copending application, Ser. No. 714,358 is effective in confining electron flow in the desired channels while discouraging electron flow and multiplication in the space between channels, it suffers from the disadvantage that it affords no relief for the situation in which an electron skips from one channel to an adjacent channel. This can be further appreciated by the fact that, in the previously discussed embodiment, in which the cathode electrode is used for addressing purposes, all of the channels along a single pair of insulating vanes (not just the "on" channel(s)) are generally in a high multiplier gain condition. This means that any electrons which manage to get out of the confinement channel and into an adjacent channel ("off" channel) will be multiplied and accelerated toward the screen, causing a loss of spot resolution and an undesirable output. Although the previously discussed structure is quite effective in minimizing the number of electrons which are able to pass through to adjacent "off" channels, the presence of these remaining electrons is amplified by two factors. One factor is the previously discussed multiplication factor. Another factor is that the resulting gain in the "off" channels is not degraded by space charge saturation means as is the case in the higher current "on" channel.
Thus, it would be desirable to develop an electron multiplier structure in which the advantages of the electron beam confinement structure shown in copending application, Ser. No. 714,358, are maintained but which further includes the ability to substantially prevent the multiplication of electrons in "off" channels which are adjacent to "on" channels.